1. Field of the Invention
The present invention relates to a power assist device for a steering apparatus which uses the rotational output of a motor for assisting the steering wheel with the steering force.
2. Prior Art Description
The steering mechanism of an automotive vehicle generally employs a pinion formed at the top end of a steering shaft with a steering wheel mounted thereon. When the steering wheel is operated, the rotation thereof is converted into a linear motion of a rack in mesh with the pinion along the transverse direction of the vehicle, whereby the left and right wheels are steered.
The power assist device for assisting the steering wheel in the steering operation includes an electric motor, a reduction mechanism for reducing the speed and outputting the rotational force of the motor, and a pinion rotated by the rotational output of reduced speed. This pinion is in mesh with the aforementioned rack for steering. A planetary gear mechanism is generally employed as the reduction mechanism.
Also, a distortion sensor is mounted on the steering shaft side of the pinion. The signal detected by the distortion sensor is supplied to a controller. The controller, on the other hand, controls the drive of the electric motor based on the detection signal, and thus can generate an optimum assisting force corresponding to the steering force.